Sex and intoxication.
Did that get your attention?
Well, this article is probably not what you think. We’re focusing on the less salacious but still very important issue of a person’s gender as a significant factor in alcohol impairment – a big deal when it comes to impaired driving. Rather than responding to a single question, this article is prompted by conversations I’ve had with people about impairment levels and driving.
Over the past couple decades, alcohol-impaired driving has steadily been decreasing (while drug impaired driving has been increasing – a topic for a future article). However, the reduction in impaired driving doesn’t apply to women. In a recent 10-year period, DUI arrests for men decreased by 7.5 percent while DUI arrests for women increased by 28.8 percent.
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You might be wondering, “If men are getting arrested 7.5 percent less and women are getting arrested 28.8 percent more, wouldn’t the overall arrest rate increase?” If we had started at an equal point that would be true. But men are guilty of impaired driving at a much higher rate than women. Even with the narrowing gap, men outnumber women as impaired drivers about 3-1.
Researchers have a variety of theories about why more women are getting arrested for DUI. Is it a cultural shift? An increase in women driving? A change in enforcement? But on one factor they agree: Biology influences impairment. A person’s weight and the rate at which alcohol is metabolized by the body top the list of impairment factors, and when it comes to impaired driving, women are at a disadvantage on both accounts.
According to the CDC, the average weight of an American man is 196 pounds, while the average American woman weighs 166 pounds. Also, because of differences in enzymes, hormones and body fat percentages between men and women, women generally metabolize alcohol at a slower rate. Simply put, women get drunk faster and stay drunk longer than men.
Let’s imagine that the average American man and woman go on a dinner date and have three glasses of wine over the course of a one-hour meal. As they leave the restaurant, the man will have a blood alcohol content (BAC) of around .06 while the woman’s BAC will be around .09. A driver is presumed to be impaired at .08. The same behavior results, in this case, in a 50 percent higher level of impairment.
I should clarify that these are just estimates, as alcohol impairment also is influenced by food intake, sleep (or lack of it), stress, drinking history, medications, illness and genetics. The point is, it’s important to recognize that biology affects impairment.
Back to our average American couple. Both the man and the woman have consumed enough alcohol to potentially be arrested for DUI if either of them drove. “Hold on a minute,” you might ask, “Didn’t you just say that a driver is presumed to be impaired at .08?”
Yes, I did, and thank you for bringing up a common misunderstanding. Our state law considers a BAC of .08 to be the point at which, from a legal perspective, anyone is impaired. Practically, that means that anyone with a BAC of .08 or higher can be arrested for DUI with no other evidence beyond a blood or breath test.
In order to arrest someone with a BAC of less than .08 for impaired driving, an officer would need to observe additional evidence. This could include erratic driving behavior, lack of coordination and poor performance on sobriety tests.
To be clear, both of our imaginary people in this example shouldn’t drive. A BAC of .06 will cause impairment. It’s a big enough concern that legislators in some states, including Washington, have proposed reducing the legal limit to .05.
But the level of impairment between a BAC of .06 and .09 is significant. According to a study of impaired driving crashes, a driver with a BAC of .06 is about 1.6 times more likely to cause a crash than a sober driver. For a driver with a BAC of .09, that jumps up to 3.5 times more likely.
Our individual biology is a major factor in how alcohol affects each of us, so I’ll leave you with two tips: Don’t judge your own impairment based on how someone else handles the same amount of alcohol, and always have a plan for a safe ride home before going out for drinks.
Road Rules is a regular column on road laws, safe driving habits and general police practices. Doug Dahl is the Target Zero Manager for the Whatcom County Traffic Safety Task Force. Target Zero is Washington’s vision to reduce traffic fatalities and serious injuries to zero by 2030. For more traffic safety information visit TheWiseDrive.com. Ask a question.